The present invention relates to an electronic musical instrument and particularly an electronic musical instrument utilizing a musical tone synthesis system of a pitch synchronous sampling type.
In conventional digital electronic musical instruments, a musical tone waveform amplitude is sampled at given sampling intervals to synthesize a tone waveform. The musical tone synthesis systems adopting sampling include (1) a pitch asynchronous technique and (2) a pitch synchronous technique. According to the former technique, an input signal is sampled at a given sampling frequency irrespective of a frequency of a musical tone to be produced. Therefore, in order to accurately produce pitches or waveforms of musical tones all having different pitches, number of amplitude data samples are required for one period of the musical tone, or a very high sampling frequency must be set. Even if the sampling timing can be applied to any phase angle, a great amount of amplitude data samples must be prepared to respectively correspond to the small phase angles, or the high sampling frequency is used to set a timing of change in the readout address. However when a great number of amplitude data samples are prepared, the required capacity of a waveform data memory is increased. In particular, when different waveform data for a number of different tone colors are stored in the memory, the required capacity becomes greatly increased, resulting in high cost and a large size. In addition, when the sampling frequency is increased too much, one-cycle sampling time of digital/analog (D/A) conversion of the musical tone signal corresponding to one-sampling time must be shortened, so that an expensive high-speed D/A converter must be used. However, such a D/A converter is expensive and has technical limitations in high-speed operation. While according to the latter technique, that is, a pitch synchronous technique, the sampling frequency is synchronous with a frequency of a musical tone to be produced. Although the problem raised by the pitch synchronous technique is relatively improved, jitter noises (an external noise components other than the musical tone signal) included in the musical tone signal to be produced is a significant problem. A countermeasure must be taken to eliminate the jitter. On the other hand, in the conventional pitch synchronous technique, sampling is performed at different sampling frequencies respectively corresponding to different pitches (different notes). When polyphonic tones are to be produced, tone generators are arranged to generate the respective single tones paralelly. As a result, polyphonic tones cannot be produced in accordance with a time division scheme. In addition to this disadvantage, the apparatus as a whole becomes large in size.